1. Field of the Invention
The present invention relates to an electric rotating machine for a vehicle having a turning angle detector and, more particularly, to a technology for improving accuracy in detecting turning angle of the turning angle detector.
2. Description of the Related Art
In general, an electric rotating machine for a vehicle is used as a synchronous motor at the time of starting an engine and is also used as an ac generator during stopping the engine. In particular, in the case where the electric rotating machine is used as asynchronous motor at the time of starting the engine and, it is necessary to control timing of applying an electric current to each field coil wound round a stator core and a rotor core. Therefore, hitherto, a turning angle detector is mounted on one shaft end part side of a rotary shaft to which the rotor core is fitted, thereby detecting a turning angle.
In this type of electric rotating machine for a vehicle, in the case of using a magnetic turning angle detector or a resolver as the above-mentioned turning angle detector, the rotary shaft is magnetized by the application of an electric current to the rotor coil wound round the rotor core. As a result of this, it has been often the case that detection accuracy of the turning angle detector is influenced by leakage flux flowing through the rotary shaft.
To overcome this disadvantage, an attempt has been proposed, in which magnetic bypass members of high-permeability are disposed in such a manner as to project outwardly in radial direction holding a magnetic turning angle detector at the front and rear parts thereof along the axial direction. Thus, leakage flux flowing through the rotary shaft is bypassed via the magnetic bypass members, thereby preventing the leakage flux from flowing through a space between Hall element and permanent magnet constituting the turning angle detector. (See the Japanese Patent Publication (unexamined) No. 2002-171723 (pages 1 to 6, FIGS. 1 and 2), for example).
In the construction disclosed in this Japanese Patent Publication (unexamined) No. 2002-171723, the leakage flux flowing through the space between the Hall element and permanent magnet constituting the magnetic turning angle detector is reduced. As a result, it is possible to improve detection accuracy of the turning angle detector to a certain extent.
However, there still is a room for improvement in the construction disclosed in the Japanese Patent Publication (unexamined) No. 2002-171723 as follows:
(1) It is necessary to additionally install the high-permeability magnetic bypass members. Therefore, there is an increase in number of parts eventually resulting in a complicated construction as a whole.
(2) The inner magnetic bypass member near the rotor core side, which is one of the magnetic bypass members disposed in front and rear of the magnetic turning angle detector, is fixed onto a side wall of a housing. Therefore, a gap is formed between the inner magnetic bypass member and the rotary shaft. The outer magnetic bypass member fixed onto an end of the rotary shaft is mounted on a retainer made of a non-magnetic material. As a result, the advantage of bypassing the leakage flux through the magnetic bypass members is not always sufficient, and there is a limit in improving detection accuracy of the turning angle detector.